Rain - a valuable resource

With water conservation high on the agenda, Andy Thompson looks at the latest developments in rainwater harvesting.

Thanks to the introduction of mains water piped directly into their homes, Victorians soon dispensed with harvesting rainwater from the roofs of their buildings. Yet, 100 years on, the concept of capturing rainwater for non-potable uses is now firmly back on the agenda, and is expected to become a major part of new-build projects going forward in the UK - credit crunch permitting.

Indeed, sales of rainwater harvesting equipment have gone up by 300% in the past two years alone, and are continuing to rise. Several drivers have been pushing the use of this cost-effective and simple technology over the past 12 to 18 months or so.

Conserving water stocks has now become a priority for architects, builders and developers to achieve an excellence rating against criteria set by the BRE Environmental Assessment Method (BREEAM) and The Code for Sustainable Homes. To achieve ratings at the higher end of the code, they must install more water-friendly appliances and rainwater harvesting to reduce water consumption in the property from an average of 1,60l per person a day, to as little as 80l.

Code level 3 became mandatory in mid-2007 for the public sector, and will be mandatory for the private sector in 2010, while levels 4 to 6 are phasing in over the next few years. However, many developers are already achieving level 3 to 4, and some are aiming for level 6.

Further legislation covering rainwater harvesting is in the pipeline. The latest Building Regulations G comes into effect from October 2009, and aims to introduce into Building Regulations for the first time a water efficiency standard of 125l per person a day for new homes. It will also clarify where greywater and harvested rainwater can be safely used.

But rainwater harvesting is not just about saving water. It also has a part to play in flood prevention, which remains an ever-present, unwelcome side effect of global warming in many parts of the country. Planning policy statement PPS25, which came into force in 2008, now requires planning authorities to undertake strategic flood risk assessments as part of their development planning.

For planning authorities, the value of including rainwater recycling systems in an application is that they reduce surface run-off during heavy rainfall. They pass the recycled water indirectly via reuse applications to the foul system rather than the storm drains, posing a slightly reduced flood risk.

Developers can achieve Code Level 6 with rainwater harvesting alone, but only if the roof area allows sufficient collection - for some eco-town / small homes this simple technology needs to supplemented.

Modern high-density housing means the average roof area is around 90m2, which represents a significant restraining factor on capacity. We need to support rainwater harvesting from roofs with additional supplies if we are to achieve the levels required by the Code, and for this we must consider water reuse or greywater recycling systems that filter and collect bath and shower water for loo flushing and garden irrigation.

Size concernsConcerns about the size of greywater filtration plants for domestic applications - which up to now have been as large as American-sized fridges - and the quality of the water they provide led to the launch of Kingspan Water's Ezy-Filter last year.

This neat little gadget, about the size of a champagne bottle, connects to a dedicated downpipe on an outside wall and treats soap, detergents and other impurities from bath and shower water, giving clear water. This can then be stored in a water butt or passed into a rainwater harvesting tank, such as a Kingspan Water 700l rainwater tank or an Envireau underground rainwater tank, and used on flower beds, for flushing loos, or for washing clothes and vehicles - in fact a range of tasks, with the exception, of course, of drinking.

Used with rainwater harvesting, greywater recycling can double the water savings for an average household, reducing the per capita usage of mains water to just 80l on average - the target for Code Level 6.

As more rainwater harvesting equipment comes on to the market, there is a pressing need to instill early consumer confidence in the technology and the quality of the resulting water.

Achieving this requires the application of British Standards, and Mike Norton, Kingspan's technical director and chair of the UK Rainwater Harvesting Association, has devoted considerable time over the past 12 months to help draft one for rainwater harvesting.

The result, BS8515 for Rainwater Harvesting, was published in January 2009. It aims to ensure comfort to specifiers and consumers, and compliance by suppliers, to minimum standards. It also addresses any concerns about the possibility of cross-contamination of mains drinking water with rainwater.

Meanwhile, any concerns about the quality and purity of greywater should be alleviated - the new British Standard BS8525 for greywater will be introduced later in 2009.

Norton is also calling for a national training programme to ensure installation standards meet minimum criteria. Anecdotal evidence suggests many supplier complaints are not down to issues with design but to poor or incomplete installation. This represents a major cost to the industry in terms of warranty payments, and needs to be addressed - trust in the sector must not be undermined before it is fully established.

To conclude, rainwater harvesting provides a viable means of conserving water and making the best use of a resource that we can no longer afford to pour down the drain.